The present invention relates to circuitry incorporated in a system including a plurality of signal processing circuits having an identical function for switching them over.
A system including a plurality of signal processing circuits having an identical function additionally includes a standby signal processing circuit. When any one of the active signal processing circuits fails, it is replaced with the standby signal processing circuit to insure the reliability of the system. However, this kind of system is totally shut down when the standby signal processing circuit substituting for the failed circuit fails itslef. While a number of standby circuits may be incorporated in the system to cope with the above occurrence, such an approach is not desirable from the cost standpoint since standby circuits are simply useless so long as the other circuits are normal.